The Bcl-2 protein contributes to both oncogenesis and intrinsic cancer treatment resistance by inhibiting apoptosis. Research supported by this grant is investigating one particular aspect of Bcl-2's mechanism of action, the inhibition of calcium signals that promote apoptosis. We discovered that Bcl-2 interacts with the inositol 1,4,5-trisphosphate receptor (IP3R), an IP3-gated calcium channel on the endoplasmic reticulum (ER), thus inhibiting IP3-induced calcium elevation. In the current funding period we used FRET to demonstrate this interaction in cells and mapped the interaction sites on both Bcl-2 and the IP3R. Based on this information we developed a peptide inhibitor of Bcl-2-IP3R interaction, Peptide 2. This peptide, when delivered into cells, reverses the inhibition of pro-apoptotic calcium signals by Bcl-2 and triggers prolonged calcium oscillations that elevate the pro-apoptotic protein Bim. The present proposal continues this work by investigating the fundamental mechanism by which Bcl-2-IP3R interaction regulates IP3R channel activity and thus inhibits IP3- dependent calcium elevation. Also, this proposal investigates the mechanism by which Peptide 2-mediated inhibition of Bcl-2-IP3R interaction triggers calcium oscillations and increases Bim levels. Finally, this proposal explores the concept of targeting Bcl-2-IP3R interaction for treatment of Bcl-2 over-expressing cancers, including chronic lymphocytic leukemia, in synergy with other therapeutic agents. PUBLIC HEALTH RELEVANCE: Bcl-2 is a very important protein that contributes to cancer. It functions to inhibit the death of cells. Therefore, when cancer cells have too much of this protein they fail to die. Thus, the cancer cells accumulate and are resistant to treatments designed to induce cell death. This proposal is for research to better understand how Bcl-2 inhibits cell death. The goal is to understand how Bcl-2 interacts with and regulates channels that conduct calcium ions within cancer cells. These ions are important in mediating cell death. Our research is investigating the hypothesis that Bcl-2 closes these channels and thus prevents the calcium ion from inducing cell death. By understanding this process we may be able to develop new treatments for cancer that overcome the cell death inhibiting function of Bcl-2.